1. Field of the Invention
The present invention relates to a laser processing apparatus for applying a pulsed laser beam having a transmission wavelength to a workpiece held on a chuck table moving in a feeding direction, thereby forming a modified layer inside the workpiece.
2. Description of the Related Art
A silicon reservoir substrate is connected to a nozzle substrate having a plurality of nozzles for discharging ink, which constitute a so-called inkjet head. The silicon reservoir substrate is formed with a plurality of through holes respectively communicating with the plural nozzles of the nozzle substrate. In forming the plural through holes in the silicon reservoir substrate, the front side of the silicon reservoir substrate is first covered with an etching mask having a plurality of openings respectively corresponding to hole forming areas where the through holes are to be formed. Thereafter, a pulsed laser beam having a transmission wavelength to the silicon reservoir substrate is applied through the openings of the etching mask to the silicon reservoir substrate, thereby forming a plurality of modified layers inside the silicon reservoir substrate at the hole forming areas. Thereafter, an etching liquid is supplied through the openings of the etching mask to the silicon reservoir substrate, thereby making the etching liquid penetrate into the silicon reservoir substrate along the modified layers. Thus, the proper through holes each having a diameter of 5 to 15 μm are formed in the silicon reservoir substrate (see Japanese Patent Laid-open No. 2010-221527, for example).